ZnO is an inorganic semiconductor with applications in large-area photovoltaics and transparent electronics. Producing ZnO thin films with excellent electronic properties is challenging and has required a series of processing tools including vacuum deposition techniques, such as rf magnetron sputtering, and post-deposition annealing in controlled gas environments. ZnO thin films can be produced from solution-deposited precursors, enabling new technologies such as printing of electronic circuits and deposition in continuous industrial processes rather than batch processes. However, since such films are dominated by defects and impurities, the electronic properties of these films must be enhanced via subsequent processing steps. Common strategies include high-temperature annealing in either hydrogen gas environments or in the presence of a hydrogen-rich capping layer, which increases the carrier concentration by introducing hydrogen into the ZnO and creates shallow donor states. Removing oxygen-vacancy donor states by annealing in an oxygen-rich environment has the opposite effect, reducing the carrier concentration. The high-temperature processing steps typically involve temperatures at 350-600° C.